JPH0576692B2 - - Google Patents

Description

[Detailed description of the invention]

1. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks. 2. Prior Art Generally, magnetic recording media are manufactured by applying a magnetic paint containing magnetic powder, binder resin, etc. onto a support and drying it. It is well known to use urethane resin as a binder resin for the magnetic layer of such magnetic recording media. Conventionally known urethane resins are synthesized from polymeric diols, diisocyanates, chain extenders, and crosslinking agents (used as necessary). Examples of the polymer diol include polyester diol obtained from adipic acid, butane diol, etc., polyether diol, and polycarbonate diol, and examples of the diisocyanate include diphenylmethane diisocyanate. Further, the chain extender may be ethylene glycol, butanediol, etc., and the crosslinking agent may be polyols, polyamines, etc. However, such general urethane resin,
Although it has excellent flexibility, the lack of hardness results in poor mechanical strength of the magnetic recording medium against sliding contact with guide pins, magnetic heads, etc., and there are also problems in terms of runnability and powder shedding. There is. 3. Object of the Invention The object of the invention is to provide a magnetic recording medium that has appropriate flexibility, sufficient mechanical strength and durability, has excellent running properties, and has little powder falling off. 4 Structure of the invention and its effects That is, the present invention provides a magnetic recording medium comprising a coating film provided on a non-magnetic support, in which the coating film is made of a first urethane resin having no yield point and 600
It is constructed using at least a second urethane resin having a yield point in a stress range of Kg/cm ² , and the ratio of the first urethane resin to the second urethane resin is 9:1 to 1:9 by weight. The present invention relates to a magnetic recording medium characterized by the following. According to the present invention, a urethane resin having a yield point is used as one of the binder resin components, but this urethane resin has the characteristics of a urethane resin without a yield point as shown by curve a in FIG. Compared to curve b, urethane resin has a yield point YP, and until the yield point YP is reached, the elongation is very small even when stress is applied. It exhibits the property of elongating with stress without breaking after the yield point YP. On the other hand, the other urethane resin used in combination with this urethane resin has a flexible property that stretches continuously under stress, as illustrated by curve a in Figure 1, and this allows the layer to have appropriate flexibility and binding strength. Contributes to the grant. Therefore, according to the present invention, if both of the above-mentioned urethane resins are used together, while exhibiting appropriate flexibility,
The mechanical strength of the magnetic recording medium is improved, damage such as wear during sliding contact, powder falling, etc. are significantly reduced, and running properties are also significantly improved. In particular, VTR
The magnetic tape used for this purpose has no edge bending, and can retain the control track near the edge and perform its function well. Above yield point
YP is important for the performance of the urethane resin of the present invention, and is 50-600Kg/ ^cm2 , preferably 100-560Kg/cm2.
Stress range of Kg/cm ² (approximately 290Kg/cm ² in the example shown in Figure 1)
It is important that there is a yield point at If the stress in the range where the yield point exists is less than 50 kg/cm ² , the resin tends to become soft, and if it exceeds 600 kg/cm ² , the resin tends to become hard and brittle. In order to exhibit the above-mentioned excellent performance, the urethane resin used in the present invention preferably has a cyclic hydrocarbon residue in the molecule. The cyclic hydrocarbon residue is preferably a saturated cyclic hydrocarbon residue, such as a divalent or monovalent cyclopentyl group, a cyclohexyl group, etc., or a derivative thereof (for example, an alkyl group substituted product such as a methyl group, Examples include those consisting of a halogen substituted product such as a chlorine atom. These saturated cyclic hydrocarbon residues are desirable from the viewpoint of imparting appropriate hardness to the urethane resin and availability of raw materials. Further, the bonding position of this cyclic hydrocarbon residue is preferably in the main chain of the urethane resin molecule, but it may be bonded to the side chain thereof. In addition, by changing the amount of components having cyclic hydrocarbon residues in the urethane resin, it is possible to obtain a urethane resin with an arbitrary glass transition point (Tg), and the Tg ranges from -30℃ to 100℃. °C, preferably 0 °C to 90 °C. If the Tg is lower than -30°C, the film will be too soft and it will be difficult to obtain sufficient film strength, and if the Tg is higher than 100°C, the film will tend to become brittle. Both of the above-mentioned urethane resins are preferably contained in the layer in an appropriate blending ratio in order to obtain good effects when used in combination. That is, the blending ratio of the urethane resin having a yield point and the urethane resin not having a yield point is preferably 9:1 to 1:9 by weight. Outside this range, if the former urethane resin decreases, the hardness of the layer tends to be insufficient due to the softness of the conventional urethane resin, and if the former urethane resin increases, the hardness of the layer tends to be insufficient. Compatibility problems are likely to occur. The urethane resin used in the present invention can be synthesized by reacting a polyol and a polyisocyanate. At this time, the following methods (1) to (4) can be employed to introduce the above-mentioned cyclic hydrocarbon residue. A urethane resin without a yield point can be synthesized by using the above-mentioned starting materials free of cyclic hydrocarbon residues in the following method. (1) A method in which a polyhydric alcohol that already has a cyclic hydrocarbon residue is used as a raw material for a polyol (for example, a polymeric diol). (2) A method in which a dicarboxylic acid having a cyclic hydrocarbon residue in advance is used as an organic dibasic acid (dicarboxylic acid) that is a raw material for the polyol. (3) A method using the polyhydric alcohols and dicarboxylic acids of (1) and (2) above as raw materials for polyols. (4) A method of using a polyhydric alcohol having a cyclic hydrocarbon residue in advance as a chain extender, in combination with any of (1) to (3) above, or alone. For example, as a synthesis method for obtaining the above urethane resin, 1,4-di-hydroxymethylcyclohexane

The polyester polyol obtained from [Formula] and adipic acid (HOOC-(CH ₂ ) ₄ -COOH) is converted into methylene-bis-phenyl isocyanate.

An example of this method is to convert it into urethane using [chemical formula]. In this case, the chain extender is the above-mentioned 1,4-di-hydroxymethylcyclohexane or other diols (e.g. butane-
1,4-diol). As the polyhydric alcohol which may have a cyclic hydrocarbon residue in advance, those having a cyclohexyl group in the molecular chain having an ethylene glycol structure can be used as described above, but in addition to such a structure, propylene glycol, Glycols such as butylene glycol, diethylene glycol, trimethylolpropane, hexanetriol,
Polyhydric alcohols such as glycerin, trimethylolethane, and pentaerythritol, or their glycols, or those having a cyclic hydrocarbon residue in their structure can be used. In addition, usable dibasic acids include phthalic acid, dimerized linoleic acid,
Examples include aleic acid, etc., or those having a cyclic hydrocarbon residue in the molecule. Instead of the above polyols, lactone polyester polyols synthesized from lactams such as s-caprolactam, α-methyl-1-caprolactam, s-methyl-s-caprolactam, and γ-butyrolactam; or ethylene oxide, propylene oxide, Polyether polyols synthesized from butylene oxide and the like may also be used. These polyols are reacted with isocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, metaxylylene diisocyanate, etc.
In this way, urethanized polyester polyurethane and polyether polyurethane are synthesized. These urethane resins according to the present invention are usually mainly produced by the reaction of polyisocyanate and polyol, and free isocyanate groups and/or hydroxyl They may be in the form of urethane resins or urethane prepolymers containing these groups, or they may be free of these reactive end groups (for example in the form of urethane elastomers). In addition, usable chain extenders include the polyhydric alcohols listed above (which may or may not have a cyclic hydrocarbon residue in the molecule).
That's fine. In addition, if a phenoxy resin and/or a vinyl chloride copolymer is also included as a binder resin in addition to the above-mentioned urethane resin, the dispersibility of the magnetic powder will be improved when applied to the magnetic layer, and its mechanical strength will be increased. do. However, if the phenoxy resin and/or vinyl chloride copolymer is used alone, the layer becomes too hard, but this can be prevented by containing polyurethane, and the adhesion to the support or base layer is improved. The phenoxy resin that can be used is a polymer obtained by polymerizing bisphenol A and epichlorohydrin, and is represented by the following general formula.

[C] (However, n82-13) For example, PKHC manufactured by Union Carbide,
There are PKHH, PKHT, etc. In addition, the above-mentioned vinyl chloride copolymers that can be used have the general formula:

[ka] There is something expressed as in this case,

The molar ratio derived from l and m in the formula is 95 to 50 mol % for the former unit and 5 to 50 mol % for the latter unit. Further, X represents a monomer residue copolymerizable with vinyl chloride, and represents at least one monomer residue selected from the group consisting of vinyl acetate, vinyl alcohol, maleic anhydride, etc.
Represents a species. The degree of polymerization expressed as (l+m) is preferably from 100 to 600; when the degree of polymerization is less than 100, the magnetic layer etc. tend to become sticky, and when it exceeds 600, dispersibility deteriorates. The vinyl chloride copolymer described above may be partially hydrolyzed. The vinyl chloride copolymer is preferably a vinyl chloride-vinyl acetate copolymer (hereinafter referred to as
It is called "vinyl chloride-vinyl acetate copolymer." )
can be mentioned. Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-vinyl acetate-maleic anhydride copolymers, etc. Among the copolymers, partially hydrolyzed copolymers are preferred. Above vinyl chloride
Specific examples of vinyl acetate copolymers include “VAGH” and “VYHH” manufactured by Union Carbide;
"VMCH", "Esretsu A" manufactured by Sekisui Chemical Co., Ltd.,
“Eslec A-5”, “Eslec C”, “Eslec M”, “Denkabinil” manufactured by Denki Kagaku Kogyo Co., Ltd.
1000G", "Denkabinir 1000W", etc. can be used. In addition to the above, cellulose resins can be used as the binder resin, such as cellulose ethers, cellulose inorganic acid esters, cellulose organic acid esters, and the like. As the cellulose ether, methyl cellulose, ethyl cellulose, etc. can be used. As the cellulose inorganic acid ester, nitrocellulose, cellulose sulfate, cellulose phosphate, etc. can be used. Also,
As the cellulose organic acid ester, acetyl cellulose, propionyl cellulose, butyl cellulose, etc. can be used. Among these cellulose resins, nitrocellulose is preferred. In addition, regarding the entire binder composition, the ratio of the above-mentioned urethane resin to other resins (total amount of phenoxy resin, vinyl chloride copolymer, etc.) is 90/10 to 35/65 by weight. It has been confirmed that 85/15 to 40/60 is more desirable. Outside this range, if the amount of urethane resin is too large, dispersion tends to be poor, and if the amount of other resins is too large, the surface properties tend to be poor, and especially if it exceeds 60% by weight, the physical properties of the coating film become less favorable overall. In the case of vinyl chloride-vinyl acetate, it can be mixed with the urethane resin with considerable flexibility, preferably 15 to 75% by weight of the urethane resin. In addition to the binder resins mentioned above, thermoplastic resins, thermosetting resins, reactive resins, and electron beam curable resins may be used as binder resins for the layers constituting the magnetic recording medium of the present invention. As a thermoplastic resin, the softening temperature is 150℃ or less,
Average molecular weight is 10000~200000, degree of polymerization is about 200~
About 2000, for example, acrylic ester.
Acrylonitrile copolymer, acrylic ester-vinyl chloride copolymer, acrylic ester-
Styrene copolymers and the like are used. The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Moreover, among these resins, those which do not soften or melt before the resin is thermally decomposed are preferable. Specifically, for example, phenolic resin, epoxy resin, urea resin, melamine resin,
Alkyd resin etc. Examples of the electron beam irradiation-curable resin include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, and polyester acrylic type. In the magnetic recording medium of the present invention, carbon black may be further added to the layer containing the urethane resin. This carbon black is preferably electrically conductive, but a light-shielding material may also be added. Examples of such conductive carbon black include Conductex 975 manufactured by Columbia Carbon (specific surface area 250).
m ² /g, particle size 24 mμ), Conductex 900 (specific surface area 125 m ² /g, particle size 27 mμ), Cabot Vulcan XC-72 (specific surface area 254
m ² /g, particle size 30 mμ), Raven 1040, 420, #44 manufactured by Mitsubishi Kasei Corporation, etc. Examples of light-shielding carbon black include Laben 2000 (specific surface area 190 m ² /g, particle size 18 mμ) manufactured by Columbia Carbon Co., Ltd.
2100, 1170, 1000, Mitsubishi Kasei Corporation's #100, #75,
#40, #35, #30 etc. are available. Carbon black should have a particle size of 20 to 30 mμ, preferably 21 to 29 mμ, but its oil absorption is 90ml.
(DBP)/100g or more is desirable because it facilitates the formation of a structured structure and exhibits higher conductivity. The above-mentioned layer containing a urethane resin having a cyclic hydrocarbon residue and a urethane resin not having the same residue as a binder resin may be the magnetic layer 2 of the support 1, as shown in FIG. 2, for example. . magnetic layer 2
A BC layer 3 is provided on the opposite side.
(The BC layer may or may not be provided.) The magnetic powder used for the magnetic layer 2, especially the ferromagnetic powder, is γ-Fe ₂ O ₃ , Co-containing γ-
Iron oxide magnetic powder such as Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ ; Fe, Ni, Co, Fe-Ni-Co alloy, Fe-Mn-
Zn alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-Co-Ni-P alloy, Co-Ni alloy etc. Fe,
Examples include various ferromagnetic powders such as metal magnetic powders containing Ni, Co, etc. as main components. In addition, a known lubricant (for example, palmitic acid), a known dispersant (for example, powdered lecithin), an abrasive (for example, fused alumina), an antistatic agent (for example, graphite), etc. are added to the magnetic layer 2. It's fine. Note that the BC layer 3 may also contain the above urethane resin. In addition, examples of the non-magnetic powder contained in the BC layer 3 include carbon black, silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, zinc oxide, α-
Examples include those made of Fe ₂ O ₃ , talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbonate, etc., preferably carbon black (especially conductive carbon black) and/or titanium oxide. It will be done.
If these non-magnetic powders are included in the BC layer, the BC
The surface of the layer can be moderately roughened (matted) to improve its surface properties, and in the case of carbon black,
By imparting conductivity to the BC layer, an antistatic effect can be obtained. It is advantageous to use carbon black and other non-magnetic powders in combination, as it can improve surface properties (stabilize running properties) and improve conductivity. Further, the magnetic recording medium shown in FIG. 2 may be provided with an undercoat layer (not shown) between the magnetic layer 2 and the support 1, or may not be provided with an undercoat layer (not shown). Same below). Further, as the material for the support 1, plastics such as polyethylene terephthalate and polypropylene, metals such as Al and Zn, ceramics such as glass, BN, Si carbide, porcelain, and earthenware are used. In addition, when coating and forming the above magnetic layer and BC layer,
It is desirable to add a predetermined amount of polyfunctional isocyanate as a crosslinking agent to each coating material. Examples of such crosslinking agents include triphenylmethane triisocyanate, tris-(p-isocyanate phenyl) thiophosphite, polymethylene polyphenyl isocyanate, and the like, in addition to the polyfunctional polyisocyanates mentioned above. FIG. 3 shows another magnetic recording medium in which an OC layer 4 is provided on the magnetic layer 2 of the medium in FIG. This OC layer 4 is provided to protect the magnetic layer 2 from damage, etc., and for this purpose, it needs to have sufficient slipperiness. Therefore, as the binder resin for the OC layer 4, the urethane resin used for the above-described magnetic layer 2 may be used (preferably in combination with a phenoxy resin and/or a vinyl chloride copolymer). The surface roughness of the OC layer 4 is preferably set to Ra≦0.01 μm and Rmax≦0.13 μm in relation to color S/N. In this case, the surface roughness of the support 1 is Ra≦
0.01μm, Rmax≦0.13μm, smooth support 1
It is preferable to use FIG. 4 shows a magnetic recording medium configured as a magnetic disk, in which a magnetic layer 2 and an OC layer 4 similar to those described above are provided on both sides of a support 1, respectively. ) contains a binder resin whose main component is the above-mentioned urethane resin. 5 Examples The present invention will be described below with reference to specific examples. After charging the components shown in Table 1 in a ball mill and dispersing them, the magnetic paint was filtered through a 1 μm filter, 5 parts of polyfunctional isocyanate was added, and the mixture was coated on a support to a thickness of 5 μm using a reverse roll coater. The tape was supercalendered and slit into 1/2 inch pieces to make video tapes (corresponding to the numbers of each Example and Comparative Example). However, the numbers after the second column of Table 1 represent parts by weight, and "actual" after the second column represents an example, and "ratio" represents a comparative example.

【table】

[Table] The following measurements were performed on the videotapes according to each of the above examples. RF output: At 4MHz using a VTR deck for RF output measurement.
The RF output was measured and showed a decrease in value compared to the initial output after 100 playbacks. (Unit: dB). Skew value: A parameter that indicates the amount of timing deviation during image playback. After 100 playbacks, the deviation from the reference signal (a signal that scans the CRT screen at approximately 64 μsec) is measured, and the value is calculated. The smaller the
Indicates that the deviation is small and the image is not distorted. Jitter value: Using a VTR jitter meter "MK-612A" manufactured by Meguro Electronics, 30℃, 80
Jitter was measured after 0 and 100 runs under high temperature and high humidity conditions at %RH. Table 2 shows the performance of each example videotape.

【table】

[Table] From the above results, it can be seen that by incorporating both urethane resins into the magnetic layer according to the present invention, the tape performance is significantly improved.

[Brief explanation of the drawing]

The drawings show examples of the present invention, in which FIG. 1 is a curve diagram showing the stress-elongation relationship of urethane resin, and FIGS. 2, 3, and 4 are magnetic recording media according to each example. FIG. In addition, in the symbols used in the drawings, 2
...Magnetic layer, 3...Back coat layer (BC layer), 4
...This is an overcoat layer (OC layer).

Claims (1)

[Claims] 1. In a magnetic recording medium comprising a coating film provided on a non-magnetic support, the coating film comprises a first urethane resin having no yield point and a second urethane resin having a yield point in the stress range of 50 to 600 kg/ ^cm2 . The ratio of the first urethane resin to the second urethane resin is 9:1 to 9:1 by weight.
A magnetic recording medium characterized by a ratio of 1:9.